Chair base



FIG. 1 is a top perspective view of a chair base illustrating the design;

FIG. 2 is a bottom perspective view of the chair base;

FIG. 3 is a left hand side view of the chair base, the right side being a mirror image thereof;

FIG. 4 is a front view of the chair base;

FIG. 5 is a rear view of the chair base;

FIG. 6 is a top view of the chair base; and,

FIG. 7 is a bottom view of the chair base.

The broken lines of the chair base are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a chair base, as shown and described. 